A mathematical pattern has emerged from observations of energetic cosmic radio bursts, most of which have been detected by Australia's Parkes Observatory. (
CSIRO/Harvard/Swinburne Astronomy Productions)

A mathematical pattern has emerged from observations of energetic cosmic radio bursts, most of which have been detected by Australia's Parkes Observatory. (
CSIRO/Harvard/Swinburne Astronomy Productions)

Unfortunately for those of us hoping for aliens, we’ve seen so few of these radio bursts that it’s hard to say whether the “pattern” will hold up.

Blasts from the Past

These blasts of radio waves are known as fast radio bursts – extremely energetic, super-fast cosmic pulses that appear to be originating from billions of light-years away. They’re rare: Scientists reported the first burst in 2007 and have only published another 10 observations since then.

In truth, the question of what these things are can’t really be solved until we know their distances.

Astronomers estimate the bursts’ distances using something called a dispersion measure, which tracks how much interstellar gunk the signal has passed through*. Briefly, bursts that are farther away travel through more gunk than bursts that are closer, and astronomers can figure out how gunked up a signal is by studying how it arrives at Earth.

FM 187.5?

When Michael Hippke of Germany’s Institute for Data Analysis recently plotted the dispersion measures of the 11 known bursts, he and his colleagues found something surprising: All the dispersion measures are integer multiples of the same number, 187.5.

When graphed, the data certainly look compelling (see Figure 1 on page 2). The team calculated a 5 in 10,000 chance of the pattern being pure coincidence. Furthermore, no astrophysical systems that we know of can produce such a stepwise distribution of dispersion measures, the team argued.

So what’s going on? If the pattern is real, it suggests fast radio bursts are not coming from all over the universe, says astronomer Scott Ransom of the U.S. National Radio Astronomy Observatory. “In that case, they should be smoothly distributed in dispersion measure,” he says. Alternatively, the signals could be coming from closer to Earth. “[The pattern] could point to a very strange kind of radio frequency interference, I suppose,” he says.

It’s an exciting possibility. Trouble is, the trend identified in the study isn’t likely to survive – for one simple reason: Newer observations, not included in the study or reported by New Scientist, don’t fit.

Hippke and his colleagues looked at dispersion measures from the 11 fast radio bursts for which published data are available. But more bursts are waiting in the wings.

“There are five fast radio bursts to be reported,” says Michael Kramer of Germany’s Max Planck Institute for Radioastronomy. “They do not fit the pattern.” Kramer is part of the team combing through data gathered by Australia’s Parkes Observatory, where all the fast radio bursts, except for one, have been spotted so far. The paper describing those bursts is close to being submitted for review, he says.

Instead of aliens, unexpected astrophysics, or even Earthly interference, the mysterious mathematical pattern is probably an artifact produced by a small sample size, Ransom says. When working with a limited amount of data – say, a population of 11 fast radio bursts – it’s easy to draw lines that connect the dots. Often, however, those lines disappear when more dots are added.

“My prediction is that this pattern will be washed out quite quickly once more fast radio bursts are found,” says West Virginia University’s Duncan Lorimer, who reported the first burst in 2007. “It’s a good example of how apparently significant results can be found in sparse data sets.”

The probability theories on which statistical tests rely are much more powerful when data sets are larger; it becomes easier to rule out coincidence and rule in significance. That’s why scientists strive to include as many data points as possible, whether they’re studying exoplanets, tumors, rats in a maze, or enigmatic astrophysical signals of unknown origin.

“It is possible that it is only an artifact,” Hippke says, of the pattern. “I know that several new fast radio bursts have been found, yet unpublished. I’d suggest these people release the dispersion measures of these FRBs, perhaps in the form of short research notes, to decide the question.”

Alas, it seems that any potential evidence for communicating extraterrestrial civilizations is slipping away almost as quickly as it emerged.

*More information on dispersion measures: Because fast radio bursts span a range of frequencies, they contain a mix of different radio wavelengths. Higher frequency radio waves are shorter and can travel more easily through the cosmos. Lower frequency waves are longer and tend to get redirected or slowed down while passing through clouds of electrons (i.e., “gunk”).

If a fast radio burst is coming from sufficiently far away, there will be a measurable delay between the arrivals of its high- and low-frequency ingredients. That delay, which corresponds to the amount of interstellar gunk the signal moves through, is called the dispersion measure.